In recent years, energy conservation concerns have led to a proposal for a bulb-shaped lamp as a replacement for an incandescent bulb, where an LED being a semiconductor light-emitting element serves as a light source (hereinafter termed an LED lamp).
The LED lamp typically has a plurality of LEDs mounted on a mounting substrate, has the mounting substrate mounted, in turn, on an end of a case having a base at the other end thereof, and has a circuit unit for causing the LEDs to emit light (i.e., for lighting) held within the case (see Patent Literature 1).
The LEDs produce heat while emitting light, and the electronic components making up the circuit unit include components that produce additional heat as well as components prone to thermal damage. In particular, given the long useful life of the LEDs, a long useful life is also desired for the circuits lighting the LEDs.
As such, a conventional LED lamp is provided with an oversized case made of a material with good thermal dissipation properties, in order to constrain temperature increases in the LEDs and in the electronic components, and to constrain the thermal load imposed on the case by the electronic components of the circuit unit. That is, the case serves as a heat sink (see Patent Literature 1).
However, having the case serve as a heat sink leads to increased temperatures in the case itself, which increases the thermal load imposed on the circuits contained therein.
In addition, a lamp has been proposed in which a further casing for the circuits is provided within the case for holding the circuits within the circuit unit without transmitting heat from the case to the circuits. When the case is made of metal, there is a further need to insulate the case from the circuits.